The invention relates to systems and methods for monitoring the operation of rolling mills, and more particularly to such systems and methods which provide information relating to specific mill components which contribute to gauge tolerance variations in the product produced by the mill.
The invention will hereinafter be described in connection with the rolling of strips or other like flat products. It is to be understood, however, that the invention may be equally applicable to the rolling of other products, including but not limited to rounds and shapes.
The quality of the finish strip produced by modern rolling mills is dependent upon many factors, including in particular roll eccentricity of the work rolls and/or the back-up rolls and/or intermediate rolls, ovality of the rolls, and problems with the roll bearings.
The eccentricity of either the work, intermediate, or back-up rolls may adversely affect the quality of the finish strip, typically by producing a regular reoccurring variation in thickness or gauge of the material being rolled. Minimizing such tolerance variations is highly desirable because of the more efficient use of materials and the economic savings relating thereto. Consumers of the finish strip often require that the gauge of the strip be as constant as possible within predetermined tolerance limits. Therefore, it is an economic necessity for rolling mills to identify and closely monitor specific causes to tolerance variations in the finish strip.
It is desirable, therefore, to have a system for continuously monitoring the eccentricity contribution of each roll to the gauge variations of the finish strip so that the mill operators would be able to make roll changes prior to the variations in the finish strip from becoming out of tolerance. If the mill operators are able to predict the proper timing of roll changes, the result will be an overall increase in the cost effectiveness in the mill. In addition to an increase of in tolerance finished product, the mill itself will be less subject to unscheduled down time due to undetected roll problems. Furthermore, it would also be helpful to mill operators to monitor the contribution of the entering product to tolerance variations in the finished product, a factor widely ignored in the industry.
Frequency spectrum analysis has been utilized in conventional roll monitoring systems for determining roll contribution to finish strip gauge variation. Briefly, the approach involves the transformation of time domain data relating to measured finish strip gauge signals, typically provided by an x-ray gauge, a nuclear gauge, or a laser, and roll motor tachometer signals into the frequency domain. The gauge frequency data is correlated with the roll frequency data in order to identify which roll or rolls are contributing to out of tolerance finish strip.
Such systems may experience difficulties in distinguishing particular roll contribution when the rolling mill utilizes multiple rolling stands with multiple rolls in each stand. This may be caused by operating frequency harmonics of multiple rolls becoming aligned or overlapping during the correlation of the data, thus causing roll identification problems. In addition, such frequency analysis systems may experience problems when the mill is not operating at an approximate constant speed. Because of the required data sampling in frequency analysis, the effect may be the smearing, widening or indistinguishing of amplitude peaks in the frequency spectrum, thereby making it difficult or impossible to relate specific roll contribution to the out of tolerance finish strip.